This invention relates to liquid purification or separation apparatus, and more particularly, to such apparatus of the gravity separation type.
Apparatus that separates a substance of heavier density from a liquid having a lesser density are known as clarifiers. Clarifiers have wide utility and application and, in general, are of the same utility as filters, centrifugal separators, devices employing reverse osmosis principles, and gravity-operative filtering apparatus. Clarifiers are used to considerable extent in the sugar refining industry, particularly in beet sugar refineries. Clarifiers are used for clarifying carbonation juices, and for recycling water used in washing sugar beets or sugarcane to remove dirt or other foreign substances from the exterior of these agricultural products before processing.
Due to requirements of the sugar refining industry and other industries, clarifiers should incorporate a number of desirable features. First of all, the clarifier should have no moving parts, so as to secure reliable operation and provide low cost. The clarifier should be of simple construction and should allow easy access to the interior of the apparatus for cleaning the separation elements. The clarifier should occupy a small amount of physical volume to conserve space, but should provide an extremely large amount of settling surface to insure a rapid and efficient separation of the liquid from the substance of heavier density. The clarifier should provide a relatively short retention time during which the separation process occurs, consonant with the desired volume of clarified liquid necessary for particular applications.
Known prior art clarifiers have failed to achieve these characteristics, or have achieved a few of these characteristics at the sacrifice of others. For example, clarifiers employing a series of cone-like filter elements stacked in vertical columns to produce cone trees are known in the art, but this type of clarifier fails to provide high quality separation due to the non-uniform cross section of each of the cone-like filter elements. As the clarified liquid flows upward inside the cone element, the fluid flow rate increases due to the decreasing cross section of the cone element, causing some of the substance of heavier density to be carried along in the fluid flow and forced through the cone-like filter. In addition, such cone tree clarifiers are extremely difficult to clean and are very expensive to construct because of the involved design of each cone-like filter element. Another form of clarifier also known in the art which does employ a uniform cross section in the fluid flow path is a multi-stage device employing a vertical arrangement of zigzag plates. In this particular design, the clarified liquid and the material of heavier density must pass through the same filtering apertures or through the same flow channels. Because the clarified liquid and the substance of heavier density are flowing at opposite directions, a turbulence results causing a disruption of the gravity settling process which reduces the efficiency of separation, and because of the multi-stage operation, increases the retention time. Accordingly, it is an object of this invention to provide a clarifier which avoids known deficiencies of prior art clarifiers and achieves the advantageous characteristics desired in most clarifier applications.
It is an object of this invention to provide a clarifier for separating a substance of heavier density from a liquid of lesser density.
It is another object of this invention to provide a clarifier of the gravity separation type in which a relatively short retention time is required to obtain a large volume of clarified liquid.
It is another object of the invention to provide a clarifier of relatively low cost having a simple construction which allows easy cleaning of and access to the separation elements.
It is a further object of this invention to provide a clarifier of the gravity separation type which requires a relatively small volume to provide a large amount of settling surface to achieve rapid and highly efficient separation.
It is a further object of this invention to provide a clarifier of the gravity separation type in which a steady and laminar flow of clarified liquid is provided at each separation element.
It is still a further object of this invention to provide a clarifier of the gravity separation type which separates the liquid and the substance of heavier density in a manner so as to avoid remixing or turbulence.
To achieve these and other objects, the clarifier of the present invention provides a vessel having a separation portion within which a plurality of separation elements are retained in at least one pair of vertical columns. Each separation element has a uniform cross section in the direction of fluid flow which is achieved by the construction of the separation element. Each separation element generally has a vertically downward extending portion or wing and a downward and outward wing joined at an apex at a predetermined angle. Both wings are generally rectangular in shape. A predetermined number of separation apertures, each of a predetermined cross sectional area are provided near the apex. Each pair of vertical columns of separation elements is arranged such that the downward wings or portion provide a vertically extending collecting channel through which the clarified liquid will flow. As the substance of heavier density settles toward the bottom of the vessel, a gradient of specific gravity is established between the top and the bottom of the vessel, with the top having a lesser specific gravity while the bottom having the greater specific gravity. As the substance of heavier density settles the specific gravity gradient causes a buoyant or generally upward flow of the liquid as its specific gravity decreases as the substance of heavier density settles. The upward-flowing liquid encounters the downward and outward wings of the separation filter elements and the buoyancy forces the liquid toward the separation apertures to the collecting channel. The separation apertures restrict the flow into the collecting channel to a slow laminar flow to insure that the particles of the substance of heavier density will settle downward against the similar outward and downward jutting wings of the separation element below, thus causing an efficient single stage separation before the liquid enters the collecting channel. The specific gravity at each separation element in the vertical column is significant in establishing the predetermined number and predetermined cross sectional area of each of the filtering apertures.
The features of novelty which characterize this invention are pointed out with particularity in the annexed claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages will best be understood by reference to the following detailed description of the invention and brief description of the drawings.